1. Field of the Invention
This invention relates generally to a socket contact in which lead pins of an electric part are loosely inserted with a small resistance into a space defined by opposite surfaces of a first and a second elastic contact elements along the opposite surfaces, and then the lead pins are horizontally moved from this loose insertion portion so as to be clamped, and more particularly to a socket contact which is suitably used to contact, for example, a pin grid array type integrated circuit (PGA type IC) having a number of lead pins projecting downwardly from a lower surface of a socket body.
2. Brief Description of the Prior Art
Japanese Utility Model Publication No. Sho 63-4370 discloses a socket contact used for the above PGA type IC. This socket contact has a first elastic contact element and a second elastic contact element both extending in a direction opposite to the insertion direction (vertical direction) of the lead pin of the IC. A lead pin loose insertion portion is formed between opposite surfaces of the first and second elastic contact elements, and a narrowly-spaced lead pin clamping portion is formed between the opposite surfaces of the first and second elastic contact elements. The lead pin inserted into the lead pin loose insertion portion with a small pressure is moved in a horizontal direction so as to be guided into the lead pin clamping portion where the lead pin is clamped by and between the first and second elastic contact elements to achieve an electrical contact. Between the lead pin loose insertion portion and the narrowly-spaced lead pin clamping portion, a pair of normally-inclining slant sides disposed in symmetric relation to each other are formed in order to guide the lead pin into the narrowly-spaced lead pin clamping portion.
For assuring a reliable electrical contact by means of prevention of the lead pin from accidentally moving toward the lead pin insertion side, a pair of reversely inclining clamping sides forming the narrowly-spaced lead pin clamping portion are provided.
As described above, according to the prior art, since the pair of normally-inclining slant sides are formed in order to guide the lead pin from the lead pin loose insertion portion to the narrowly-spaced lead pin clamping portion and this pair of slant sides is arranged in a symmetric relation relative to each other, the first and second elastic contact elements are simultaneously pressed so as to be spread outwardly against elasticity thereof at portions between the pair of slant sides and the pair of clamping sides. As a consequence, resistances caused by the first and second elastic contact elements are applied simultaneously to the first and second elastic contact elements, and an operating force for the movement of the lead pin is overly increased.
Particularly, in the case where the clamping sides forming the lead pin clamping portion are served as the reversely-inclining slant sides as mentioned above, the space of the clamping portion must be narrower at that end where the lead pin begins to be guided in. As a result, an operating force required for moving the lead pin into the lead pin clamping portion is more increased.
In other words, by forming the clamping sides of the lead pin clamping portion as reversely-inclining slant sides, a reliable contact can be assured by means of prevention of the lead pin from accidentally moving from the lead clamping portion to the lead pin loose insertion portion. This in turn gives rise to such a problem as to increase an introduction force into the lead pin clamping portion which eventually necessitates a large operating force.